The present invention relates to an optical pickup for optically recording or reproducing data onto or from a recording medium.
An optical pickup generally includes a deflecting device to provide fine tracking control for a recording medium in recording and reproducing information.
For example, Jpn. Pat. Appln. KOKAI Publication No. 6-318331 discloses an optical pickup using a galvanomirror as a deflecting device. The optical pickup measures the deviation between the optical axis of the optical system and the center of the light beam on the basis of the track deviation signal obtained when the galvanomirror is rotated. Then, on the basis of the deviation, the amount of correction is determined. Thereafter, the galvanomirror is rotated according to the amount of correction to eliminate the deviation of the optical axis, so that accurate tracking control is assured.
Since the optical pickup, however, dose not directly sense the rotation of the galvanomirror, once a rotation of the galvanomirror becomes too large to prevent the track error signal from being sensed, accurate tracking control will be difficult to perform.
Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 5-174417 discloses the technique for directly sensing the rotation of the deflecting device by adding a beam splitter in the optical path of the optical system and directing part of the light beam to a position sensor via the beam splitter.
In this technique, however, the beam splitter has to be prepared additionally, which leads to not only a rise in the production cost but also an increase in the size and weight of the optical pickup.
Still furthermore, Jpn. Pat. Appln. KOKAI Publication No. 5-28523 discloses the following two techniques. One technique is to fix an additional light source to the mirror holder of the deflecting device and sense the light beam from the light source with an additional sensor to determine the inclination of the mirror. The other technique is to use the back of the mirror of the deflecting device as a reflecting surface, project a light beam from an additional light source onto the back of the mirror, and sense the light reflected from the back of the mirror with an additional sensor to determine the inclination of the mirror.
Jpn. Pat. Appln. KOKAI Publication No. 5-334703, which is similar to the above, discloses the technique for sensing the inclination of the mirror of the deflecting device by using a photoreflector into which a light-emitting element and a light-receiving element are integrated.
Because any one of the above techniques requires a light source or light-emitting element and a sensor or light-receiving element to be additionally prepared, this results not only in a rise in the production cost but also in an increase in the size and weight of the optical pickup.